1. Field of the Invention
The present invention relates to a piezoelectric resonator, a method of manufacturing the piezoelectric resonator, a piezoelectric filter, a method of manufacturing the piezoelectric filter, a duplexer, and an electronic communication device. More particularly, the piezoelectric resonator is used in filters, oscillators, and other suitable devices, thickness longitudinal vibrations are generated in the VHF, UHF, and higher frequency bands, and vibrating portions are provided on a diaphragm.
2. Description of the Related Art
The construction of a related piezoelectric resonator of this type includes a thin-film diaphragm that is provided on a substrate having a uniform thickness so as to cover an opening formed in the substrate. A laminated body, in which a piezoelectric thin film is sandwiched by upper and lower electrodes, is mounted on the upper surface of the diaphragm. When a voltage signal is applied between the electrodes, the laminated body as a vibrating portion resonates on the diaphragm. It becomes possible for such a piezoelectric resonator to resonate in higher frequency bands when the piezoelectric film is made thinner.
In the piezoelectric resonator of this type, the vibrating portion is spaced a fixed distance from the diaphragm fixing ends so that the vibrating portion may perform required vibrations.
Furthermore, in the case of a piezoelectric resonator in which a plurality of vibrating portions are provided on a diaphragm, the vibrating portions are located a fixed distance away from each other on the diaphragm so that the resonance characteristics of each of the vibrating portions may not be influenced by the other vibrating portions.
Then, in such a piezoelectric resonator, to make the resonator smaller, it is considered that the vibrating portions are provided so as to be close to the diaphragm fixing ends and the other vibrating portions. In this case, if the vibrating portions are too close to the diaphragm fixing ends and the other vibrating portions, etc., the size of the piezoelectric resonator can be achieved. But, they influence the vibration characteristics. To the contrary, if the vibrating portions are too far from the diaphragm fixing ends and the other vibrating portions, etc., their influence on the vibration characteristics diminishes or disappears. But, the size becomes larger. Thus, when the vibrating portions are disposed on a diaphragm, it is very difficult to achieve a highly precise position of the vibrating portions. Therefore, the performance of the piezoelectric resonator, and other devices including such a piezoelectric resonator, is degraded or its productivity becomes lower.
Such disadvantages can be also seen in the filtering characteristics of a filter in which a plurality of these piezoelectric resonators is combined.
In a dual mode filter and ladder filter, the resonators must be separated by a predetermined distance from each other so that the vibration of the adjacent resonators does not influence the other. In case of the dual mode filter, even if the resonators are separated too far from each other, the characteristics do not deteriorate. However, in the case of a ladder filter, the upper electrode or lower electrode of one resonator and the upper electrode or lower electrode of another adjacent resonator are integrally formed and they are required to be electrically connected. Therefore, if a distance between the resonators is greater than 3xcex in order to prevent vibrational interference, the wiring between the resonators is lengthened, and the resistance of the wiring and an inductance due to the wiring are generated between the resonators. As a result, the characteristics are deteriorated. In particular, if the wiring resistance is generated between the resonators connected in series, insertion loss is increased.
In order to overcome the problems described above, preferred embodiments of the present invention minimize the influence of one of the vibration portions on the resonance characteristics of the other and also minimize the total dimensions of the device.
According to a preferred embodiment of the present invention, a piezoelectric resonator includes a substrate and a plurality of vibrating portions constructed such that a thin film portion having a piezoelectric thin film of one or more layers disposed on the substrate is sandwiched between at least a pair of upper electrodes and a lower electrode, opposed to each other, on the upper and lower surfaces of the thin film portion, the vibrating portions are separated by at least about xcex/2 (xcex represents the vibration wavelength) from elements affecting the vibration characteristics.
According to this preferred embodiment of the present invention, since the vibrating portions are separated by at least about xcex/2 from elements affecting the vibration characteristics, for example, the opening end portions or the other vibrating portions, the vibration characteristics are not improperly influenced by the elements such as the opening end portions and other portions, as in the case when the vibrating portions are located too close to the opening end portions or other portions. In addition, the piezoelectric resonator has a significantly reduced size and excellent vibration characteristics.
In the above-described piezoelectric resonator of the present invention, the substrate preferably includes an opening portion or concave portion and the vibrating portions are preferably disposed in the opening portion or concave portion. The periphery of the opening portion or concave portion and the vibrating portions constitute the elements affecting vibration characteristics.
In the piezoelectric resonator of the preferred embodiments of the present invention, the vibrating portions preferably include an insulation film below the lower electrode and a beam on the lower surface of the insulation film to increase the mechanical strength of the vibrating portions and the vibrating portions are separated by at least about xcex/2 from the beam which is an element affecting the vibration characteristics. In this way, even if the vibrating portions are separated by at least about xcex/2 from the beam, a piezoelectric resonator having such a construction can be made smaller while the performance of the piezoelectric resonator or a device including such a piezoelectric resonator is maintained at a sufficiently high quality.
Preferably, in a piezoelectric resonator of preferred embodiments of the present invention, the vibrating portions are preferably separated by about 3xcex or less from the elements.
More preferably, in a piezoelectric resonator of preferred embodiments of the present invention, the piezoelectric thin film preferably includes zinc oxide or aluminum nitride as a main component.
In a method of manufacturing a piezoelectric resonator according to another preferred embodiment of the present invention, the piezoelectric resonator including a substrate having an opening portion or concave portion and a plurality of vibrating portions constructed such that a thin film portion having a piezoelectric thin film of one or more layers, which is disposed in the opening portion or concave portion, is sandwiched between at least a pair of upper electrodes and a lower electrode, opposed to each other, on the upper and lower surfaces of the thin film portion, the method includes the step of forming the vibrating portions to be separated by at least about xcex/2 (xcex represents the vibration wavelength) from elements affecting the vibrating characteristics and formed in the opening portion or concave portion.
According to preferred embodiments of the present invention, since the vibrating portions are separated by at least about xcex/2 from elements affecting the vibration characteristics, from the opening end portions or the other vibrating portions, undesired influence of the elements such as the opening end portions and other vibrating portions, on the vibration characteristics as in the case when the vibrating portions are too close to the elements which affect vibration portions is reliably prevented. In addition, a piezoelectric resonator having a greatly reduced size and excellent characteristics is provided.
In a piezoelectric filter of a preferred embodiment of the present invention including a substrate and a plurality of vibrating portions constructed such that a thin film portion having a piezoelectric thin film of one or more layers disposed on the substrate, is sandwiched between at least a pair of upper electrodes and a lower electrode, disposed opposite to each other, on the upper and lower surfaces of the thin film portion, the vibrating portions are connected so as to constitute a filter for a required frequency band, and the vibrating portions are separated by at least about xcex/2 (xcex represents the vibration wavelength) from elements affecting the vibration characteristics.
According to preferred embodiments of the present invention, since the vibrating portions are separated by at least about xcex/2 from elements affecting the vibration characteristics, for example, from the opening end portions, or the other vibrating portions, undesired influence of the elements such as the opening end portions or other portions, on the vibration characteristics as in the case when the vibrating portions are too close to the elements that affect vibration characteristics is avoided, and a piezoelectric resonator having a greatly reduced size can be easily manufactured while still having excellent characteristics.
Preferably, in the above-described piezoelectric filter, a substrate includes an opening portion or concave portion and the vibrating portions are preferably formed in the opening portion or concave portion.
The periphery of the opening portion or concave portion and the other vibrating portions constitute the elements that affect the vibration characteristics.
In the above-described piezoelectric filter, a beam is preferably provided on the lower surface of a diaphragm in order to increase the mechanical strength of the diaphragm, and, even if the vibrating portions are separated by at least about xcex/2 from the beam, the piezoelectric filter can be reduced in size in the same way as described above while the excellent performance of the piezoelectric filter is maintained.
Preferably, in the above-described piezoelectric filter, the vibrating portions are preferably separated by about 3xcex or less from the elements that affect the vibration characteristics.
More preferably, in the above-described piezoelectric filter, the piezoelectric thin film preferably includes zinc oxide (ZnO) or aluminum nitride (AlN) as a main component.
More preferably, in the above piezoelectric filter, the vibrating portions preferably constitute a ladder filter.
In a method of manufacturing a piezoelectric filter according to a preferred embodiment of the present invention, the piezoelectric filter including a substrate having an opening portion or concave portion, a plurality of vibrating portions constructed such that a thin film portion having a piezoelectric thin film of one or more layers is sandwiched between at least a pair of upper electrodes and a lower electrode, which are disposed opposite to each other, on the upper and lower surfaces of the thin film portion and formed in the opening portion or concave portion, and the vibrating portions connected to constitute a filter for a required frequency band, a process, includes a step in which the vibrating portions are formed so as to be separated by at least about xcex/2 (xcex represents the vibration wavelength) from elements affecting the vibrating characteristics.
According to preferred embodiments of the present invention, since the vibrating portions are separated by at least about xcex/2 from elements affecting the vibration characteristics, for example, from the opening end portions, the other vibrating portions, or other portions, undesired influence of the elements such as the opening end portions, other vibrating portions, etc., on the vibration characteristics as in the case when the vibrating portions are too close to the elements, is prevented, and a piezoelectric resonator having a greatly reduced size can be easily manufactured while excellent characteristics thereof are maintained.
In a duplexer according to another preferred embodiment of the present invention, a piezoelectric filter of other preferred embodiments of the present invention is used. Thus, a duplexer in which signal switching, etc., can be satisfactorily accomplished is provided.
In an electronic communication device according to another preferred embodiment of the present invention, a piezoelectric resonator of other preferred embodiments of the present invention is included. Furthermore, in an electronic communication device of another preferred embodiment of the present invention, a piezoelectric filter of other preferred embodiments of the present invention is included. As a result, an electronic communication device, in which the function of signal processing such as modulation, demodulation, etc., is excellent, is provided.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.